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Title: Pea Aphid Outbreaks and Virus Epidemics on Peas in the U.S. Pacific Northwest: Histories, Mysteries, and Challenges

item Clement, Stephen

Submitted to: Plant Health Progress
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/3/2006
Publication Date: 10/18/2006
Citation: Clement, S.L. 2006. Pea Aphid Outbreaks and Virus Epidemics on Peas in the U.S. Pacific Northwest: Histories, Mysteries, and Challenges. Plant Health Progress. doi:10.1094/PHP-2006-1018-01-RV.

Interpretive Summary: The USDA, ARS Plant Introduction Station, Pullman, Washington maintains and stores seed of over 72,000 accessions of major U.S. crops, including food legumes like peas. Curators at this facility establish field nurseries of replicate plants of accessions to replenish seed stocks low in viability and supply. This seed is provided to plant breeders in the U.S. and other countries for new cultivar development and agricultural sustainability. There are, however, hazards and practical difficulties associated with this method of seed regeneration, such as exposure to pathogens and pest insect attack. For example, pea nurseries are subject to periodic attacks by a major insect pest called the pea aphid, which also transmits at least four different pathogenic viruses to pea plants. This aphid and its transmitted viruses also reduce pea yields for farmers in eastern Washington and northern Idaho. Broad spectrum insecticides are used widely to control this aphid. This research paper by a USDA-ARS Research Entomologist at the Pullman Station contributes the first comprehensive analysis of the factors that contribute to pea aphid outbreaks on pea nurseries and commercial pea fields and, furthermore, is significant because it gives curators and farmers specific guidelines (based on winter temperatures) to predict the occurrence of non-outbreak years, which are the norm rather than the exception in eastern Washington. Pea outbreaks occurred only four times over 23 years. These results call into question the need for widespread applications of insecticides for pea aphid control in most years. Finally, this research is important because it demonstrates the value of long-term research to pinpoint the potential of insect pests to adversely impact germplasm regeneration and pea farming activities.

Technical Abstract: The pea aphid adversely affects the health and vigor of peas in the U.S. Pacific Northwest by sucking sap from leaves, stems, and pods and by transmitting four different pathogenic viruses. In eastern Washington, field peas are devastated by pea aphid feeding damage and legume viruses during periodic aphid outbreak yeas. When massive pea aphid flights arrive in this region without warning, pea producers are caught off guard and cannot implement timely control measures. Mild winters have been historically linked to widespread spring and early summer outbreaks in Oregon and Washington, with the result that present-day pea farmers and pest managers associate pea aphid problems with mild winters. In this paper, 23 years of pea aphid density and temperature data showed that mild winter temperatures alone are not sufficient to account for spring and summer pea aphid outbreaks on field peas in eastern Washington. No outbreaks occurred when there were winter days below - 9.5 C and low monthly winter temperatures averaged above -0.56 C. These temperature patterns are excellent for predicting the occurrence of non-outbreak years. During this 23 year study, four outbreaks occurred at 5-9 year intervals, thus outbreak years are the exception rather than the norm in eastern Washington. With this information, farmers can better anticipate the need for pest control measures to reduce pea aphid densities.